Hydraulic mechanisms



@m 9, 1956 A. ASHLEY ET AL 2,765,626

HYDRAULIC MECHANISMS Filed Feb. 10. 1954 27 24 27 29 g FOUR-WAY n I 25 45 32 46 VALVE 51 i Pl/Mp 26 56 3 -13 i 68 *54 P/LOT SYSTEM 335 53 56 37 DISCHARGE 585 40 39 41 VALVE Q5 75 CHECK AND 44 47 HOLD/1V6 44A 44 75 71 69 MAI/51 45 cOMPE/VsATINc J PISTON 1 67 74 75 swM DOW/V w l y I 48 704 7a P/VALVE- 11 I 64 A14 70 @2' 7o 76 WMIQMWY 2,765,626 HYDRAULIC MECHANISMS Allan Ashley and Edward Cecil Houghton, Westminster, London, England, assignors to Viclrers-Armstrongs Limited, London, England, a British company Application February 10, 1954, Serial No. 409,451

Claims priority, application Great Britain February 11, 1953 7 Claims. (Cl. 60-97) This invention relates to hydraulic mechanisms.

According to the present invention there is provided a hydraulic mechanism comprising a first hydraulic jack having a first piston and a first cylinder as main parts thereof, a second hydraulic jack having a second piston and a second cylinder as main parts thereof, wherein the first cylinder is connected to be supplied with liquid displaced from one side of the second piston, the other side of the second piston being arranged to have liquid fed thereto from a pressure source, the arrangement being such that when liquid is so fed, the first and second pistons can be thereby moved in synchronism.

For a better understanding of the invention and the method of carrying the same into efiect reference will now be made to the accompanying drawing which shows a hydraulic mechanism applied to a press.

The press has a bed 1, and a crown 2 supported above the bed 1, by means of uprights 3 which extend from the sides of the bed. A slide 4 mounted for vertical reciprocation towards and away from the bed 1 is carried by hydraulic jacks mounted in the crown 2. The end 4A from a member 9 fired on the piston rod 10 of the piston 11 of a primary main jack 5. The end 4A is also pivotally suspended from a member 12 carried on the lower end of a screw 13 secured in the piston rod 14A of the piston 14 of a pull-back jack 6. The opposite end 4B of the slide 4 is pivotally suspended from a member The hydraulic system for operating the jacks is as follows. A mam pump 23 driven through a flexible coupling 24 from an electric motor 25 draws liquid from a tank (not shown) via a pipe 26 and delivers liquid by a pipe 27 through a relief valve 28 to the inlet 29 of a four-way valve 30. When the pump delivery pressure increases tank. The plunger 33 has two wide annular grooves 40, 41 disposed one on each side of the central port 35, the annular groove 40 communicating with a port 42 through the barrel which port 42 leads via a check and holding valve 44 and a pipe 45 to the pr1mary groove 41 on the plunger municates with the valve outlet 39 to the tank via said annular groove 40 and the annular groove 53 in the barrel. When the solenoid operated valve 54 is deenergised and the other one is energised the plunger 33 tically downwards from the centre of the upper face of the piston 11. piston 63 is slidably located in this recess 62 and a spring 64 may be interposed between the compensating piston 63 and the bottom of the recess 62. The top of the compensating piston 63 is acted upon by the fluid in the upper chamber 65 of the cylinder 19. The lower portion of the recess 62 com- The upper chamber 65 of the primary main jack 5 can communicate with the tank via a discharge valve 68 and a pipe 69. The valve 63 is hydraulically operated by the liquid pressure in the pipe 47 between the port 46 of the fournvay valve 38 and the check and holding valve 44. When the pressure in the pipe 47 is low the discharge valve 63 is closed and when high pressure liquid from the main pump 23 is flowing through the pipe 47 the discharge valve 63 is opened.

The pull-back jack 7 is arranged to operate a slowdown valve 70 when the slide 4 is nearing the top of its stroke. The slow-down valve 76 is located in a leak-off pipe 71 leading from the pipe 47 to said tank. The valve 76 has lands 76A and 763 with groove 70C therebetwcen. The land 7 A of the slow-down valve 70 normally closes the leak-off pipe 71. When the piston 13 of the pullback jack 7 nears the end of its upward stroke, the piston 18 encounters a rod 72 projecting downwardly through the upper end of the jack cylinder 21 and pushes this rod 72 upwardly, thereby opening the slow-down valve 70. Continued upward movement of this piston 18 causes the land 7013 of the valve 7i) to close the pipe 71, and the top of the valve 70 encounters the stem of a normally closed replenishment valve 73 to open this valve, whereby liquid is permitted to'tlow from the pilot system 55 via a pipe 74 and a pipe 75 to the pipe 67 and vice versa. At the upper end of its stroke the piston 18 operates by means of a rod 76, a top limit switch 77 which de-energises the solenoid operated valve 54 whereby the plunger 33 of the four-way valve 30 returns to its central position. The pull-back jack 7 is connected to the check and holding valve 44, in parallel with the pull-back jack 6.

The press described above operates as follows. When neither of the solenoid operated valves 54, 56 is energised, the four-way valve 30 is in the central position and the main pump 23 discharges via the pipe 39 into said tank. The slide 4 is held by the pull-back jacks 6, 7 from which liquid cannot be exhausted through the check and holding valve 44. It will be understood that the pistons 14, 18 of the pull-back jacks 6, 7 are at the top of their stroke and these jacks are full of liquid. The replenishment valve 73 is open whereby the liquid circuit between the secondary chamber 61 of the primary jack 5, and the secondary main jack 8 can be charged by or vented to the pilot system 55'.

When the solenoid operated valve 56 is energised, the four-way valve 39 causes liquid from the pump at a. pressure sufficient to lower the slide against a' moderate resistance, to be delivered via the pipe 27, inlet 29, groove 40, port 42, pipe 43, the check and holding valve 44 and pipe 45 to the primary main jack 5. This causes the check and holding valve 44 to permit controlled flow of liquid from the pull-back jacks 6, 7 to the four-way valve 30', via the pipes 49, 50 and 48, the valve 44 and the pipe 47, from whence this liquid is returned to the tank via the pipe 39. The controlled rate at which the liquid from the pull-back jacks 6, 7 passes through the check and holding valve 44 controls the downward movement of the slide 4. The main piston 11 of the primary main jack 5 descends and as the underside of this piston is of the same area as the secondary main piston 16, the latter piston is caused to move downward at the same rate as said main piston 11. The replenishment valve 73'of course closes as soon as the pull-back jack 7 has commenced exhausting, since as soon as this occurs, the slide4, due to its weight, pulls the pistons 14, 18 of the pull-back jacks 6, 7 downwards.

If an end 4A or 4B of the slide 4 contacts the work before the opposite end, the slide 4 will hesitate until said opposite end also contacts the work, before sufficient pressure is built up in the main jacks 5, 8 for the working stroke to proceed. The slide 4 will therefore hold the work firmly over the full length before pressing egins.

When the end 4A contacts the work first, a slight increase in pressure takes place above the main piston 11 of the primary main jack and this will cause the compensating piston 63 to be forced downwardly thereby displacing liquid from the underside of the main piston 11, to the secondary main jack 3. The slide 4 is thereby caused to align itself with the work before the rising pressure above the main piston 11 becomes high enough for the reaction to be overcome. The compensating piston 63 is forced down until the load is equally divided between the two main jacks 5, 3.

if the end 48 of the slide 4 contacts the work first on account of misalignment of the slide, the compensating piston 63 will already have been displaced downwardly within its recess 62, since the piston 16 will be below its usual position in relation to the piston 11 and the hydraulic circuit between the underside of the piston and the ram 8 must remain full of liquid because this circuit is under fluid supply pressure. As the pressure in the secondary main ram 8 increases, the compensating piston 63, owing to the intensification of the pressure in the hydraulic circuit between the two main jacks 5, 8, will rise within its recess 62. The compensating piston 63 will therefore adjust itself to allow for compressibility of the liquid and metallic expansion of the closed system under pressure.

If the end 4B of the slide 4 should contact the work before the end 4A because of uneven distribution of the Work, the main piston 11 within the primary main jack 5 moves downwards until the pressure in the hydraulic circuit between the two main jacks becomes sufficient to move the secondary main jack 6 to overcome the reaction. If this reaction should remain sufficiently high to cause the main piston 11 in the primary jack 5 to reach the bottom of its stroke in advance of the secondary main jack 8, the compensating piston 63 would then move downwards to cause the secondary main jack 8 to complete its stroke.

When the slide 4 contacts the work, the pressure rises in the primary circuit and acting on the surface 44A causes the valve member 44B to move to the right so that the valve 44 opens the pipe 48 to free exhaust, thus relieving back pressure in the jacks 6 and 7 and enabling the full power of the press to be utilised.

When the slide 4 reaches the end of its downward stroke the solenoid operated valve 56 is de-energised and the solenoid operated valve 54 is energised. This change in energisat-ion may be efiected by pressure switches 78 in the hydraulic supply conduit leading to the main jack 5 or by limit switches (not shown) actuated by the slide 4'itself. When the change in energisation of the solenoid operated valves 54, 56 is effected, high pressure liquid from the main pump 23 is delivered by the four-way valve 30 through the pipe 47, the check and holding valve 44 and the pipes 48, 49, Stito the pull-back jacks 6, '7. The primary main jack 5 exhausts to the tank via the discharge valve 68 and the pipe 69, and via the check and holding valve 44 and the four-way valve 30. The liquid in the secondary main jack 3 is transferred to the primary main jack 5. The flow of liquid through the check and holding valve 44 to the pull-back jacks 6, 7 is relatively unrestricted so that these jacks operate quickly and the slide 4 is returned to the top of its stroke at high speed. As the slide 4 approaches the top of its stroke, the slowdown valve 70 is opened and some of the main pump discharge is-by-passed from the pipe 47 by way of the pipe'71 to the-tank so that the'supply of liquid to the pull-back jacks 6, 7 is reduced and the slide 4 slows down. At the top of the stroke the'top limit switch 76 is operated whereby the solenoid operated valve :74 is (lo-energised and the plunger 33 in the four-way valve 30 returns to its central position whereby liquid supply to the pull-back jacks 6, 7 is interrupted. The press is then ready to commence a further cycle.

In a modified form of the hydraulic system described above the jacks 5 and 6 are omitted and the jack '8 is in the conventional form of a cylinder and piston, the latter being received on a piston rod carrying the member 15. The chamber on the underside of this piston is arranged for connection to the chamber 61 so that liquid can be fed to these two chamber to lift the slide 4. On the lifting stroke the chamber on the upper side of the piston of the jack 8 would, of course, be connected to exhaust instead of to the chamber 61.

We claim:

1. A hydraulic mechanism for moving an element to be controlled, the mechanism comprising a first hydraulic jack having a first cylinder and a first piston in the first cylinder as main parts thereof, a second hydraulic jack having a second cylinder and a second piston in the second cylinder as main parts thereof, a first connection for supplying liquid from one end of the second cylinder to one end of the first cylinder so that the pistons move in synchronisrn, a second connection for feeding liquid from a pressure source to the other end of the second cylinder, and a compensating piston carried by the second piston and slidable longitudinally of the second cylinder with respect both to the second cylinder and the second piston, one end of the compensating piston being in communication with said one end of the second cylinder and the other end of the compensating piston being in communication with said other end of the second cylinder, the compensating piston preventing flow of liquid from one end f the second cylinder to "the other while the ends of the compensating liquid in the respective ends of the second cylinder.

2. A hydraulic mechanism according to claim 1, wherein the compensating piston is located in a longitudinal recess in the second piston.

3. A hydraulic mechanism for moving an element to be controlled, the mechanism comprising a first hydraulic jack having a first cylinder and a first piston in the first cylinder as main parts thereof, a second hydraulic jack having a second cylinder and a second piston in the second cylinder as main parts thereof, a first connection for supplying liquid from one end of the second cylinder to one end of the first cylinder so that the pistons move in synchronism, a second connection for feeding liquid from a pressure source to the other end of the second cylinder, a compensating piston carried by the second piston and slidable longitudinally of the second cylinder with respect both to the second cylinder and the second piston, one end of the compensating piston being in communication with said one end of the second cylinder and the other end of the compensating piston being in piston are acted on and movable by the communication with said other end of the second cylinder, pull-back hydraulic jack means, a pipe leading to said pull-back hydraulic 1' cl: means, a valve device in said pipe, the valve device including check valve means for controlling the leakage of liquid from said pull back hydraulic jack means, pressure responsive means for operating the check valve means, and means for subjecting the pressure responsive means to the pressure of the liquid in said second connection for feeding liquid, whereby the rate at which liquid can leak from the pullback hydraulic jack means is controlled by the pressure of the liquid fed to the second cylinder.

4. A hydraulic mechanism according to claim 3, wherein the valve device includes further pressure responsive means subjected to the pressure of the liquid in said second connection, and a valve operated by the further pressure responsive means to allow liquid to escape freely from the pull-back jack means when the pressure in said second connection reaches a predetermined amount.

5. A hydraulic mechanism according to claim 3 and further including pivotal connections between the jacks and said element and between said pull-back jack means and said element so that the element can tilt.

6. A hydraulic mechanism according to claim 3, wherein the pull back jack means includes a third cylinder and a third piston in the third cylinder, said pipe leading to one end of the third cylinder, the mechanism further including a conduit leading from said first connection to a liquid source, a further valve in said conduit, and control means at the other end of the third cylinder for opening said further valve when the third piston is adjacent said other end of the third cylinder.

7. A hydraulic mechanism according to claim 3, wherein the pull-back jack means includes a third cylinder and a third piston in the third cylinder, said pipe leading to one end of the third cylinder, the mechanism further including a leak-off pipe leading from said second connection, a further valve in said leak-off pipe, and control means at the other end of the third cylinder for opening said further valve when the third piston approaches said other end of the third cylinder.

References fitted in the file of this patent 

